Control device for the cooling system of an automobile

ABSTRACT

An electric circuit for the automatic control of the cooling system of an automobile, in which a negative resistance element such as a thermistor is incorporated as the temperature detector, and the circuit is designed so as to prevent the frosting of the cooling system due to excessive cooling which may occur if the maximum resistance of the temperature control resistor happens to be excessively high, and further to relieve the automobile engine from the burden of the cooling system during low speed operation of the engine.

United States Patent Yonezu Aug. 29, 1972 [54] CONTROL DEVICE FOR THE 3,324,352 6/1967 Hover ..307/3l0 COOLING SYSTEM OF AN 2,808,471 10/1957 Doucel et al ..307/310 x AUTOMOBILE 3,332,406 7/1967 Perry et a1. ..324/ 169 [72] Inventor: Hisashi Yonezu, Aichi, Japan Primary Emminer Don a1 d D. Ferret [73] Assignee: Nippondenso Kabushiki Kaisha, Assistant Examiner-B. P. Davis Kariya-shi, Aichi-ken, Japan Attorney-Cushman, Darby & Cushman- [22] Filed: Feb. 4, 1970 Appl. No.: 8,648

Foreign Application Priority Data Feb, 5, 1969 Japan ..44/8948 May 5, 1969 Japan ..44/41 381 References Cited UNITED STATES PATENTS 2/1967 Brace ....236/74 [57] ABSTRACT An electric circuit for the automatic control of the cooling system of an automobile, in which a negative resistance element such as a thermistor is incorporated as the temperature detector, and the circuit is designed so as to prevent the frosting of the cooling system due to excessive cooling which may occur if the maximum resistance of the temperature control resistor happens to be excessively high, and further to relieve the automobile engine from the burden of the cooling system during low speed operation of the engme.

4 Claims, 4 Drawing Figures CONTROL DEVICE FOR THE COOLING SYSTEM OF AN AUTOMOBILE BACKGROUND OF THE INVENTION 1 Field of the Invention This invention relates to automatic control devices for electrically controlling automobile cooling systems.

2. Description of the Prior Art Semiconductor heat-sensitive elements such as thermistors are extensively used in the field of temperature control, as they have a negative temperature characteristic and their resistivity depends largely upon temperature. There have, heretofore, been proposed a variety of circuits utilizing a semiconductor heat-sensitive element for the temperature control of automobile cooling systems. By way of example, one such circuit consists of a bridge circuit including a thermistor and a temperature adjustment variable resistor respectively having one terminal grounded and the other terminal connected through the respective resistors to the power source, and a transistor with the base thereof connected to the junction between the thermistor and the associated resistor while the emitter thereof is connected to the junction between the temperature adjustment variable resistor and the associated resistor. As

the ambient temperature rises, the resistance of the thermistor decreases to lower the base potential of the transistor, thus cutting off the transistor. With a fall in temperature, the resistance of the thermistor is increased to increase the base potential of the transistor, thus triggering the transistor. The circuit is constructed such that the operation of the cooling system is started by the cutting-off of the transistor and is stopped by the triggering of the transistor. The temperature adjustment for the temperature control circuit of this construction is accomplished by means of the temperature adjustment variable resistor. When the resistance of the variable resistor is zero ohms, at which the emitter of the transistor is at ground potential, the base of the transistor is triggered with a low voltage. Thus, the cooling system is stopped while the thermistor resistance is low (the temperature high), thereby presetting the temperature of the car interior at a high value. When the resistance of the variable resistor is maximum, the transistor will not be triggered unless the transistor potential is sufficiently increased. Thus, the cooling system during this time is stopped when the resistance of the thermistor has been increased (with a decrease in temperature), so that it is possible to preset the temperature of the car interior at a low value.

As is apparent, the car interior is preset to be at a high temperature when the resistance of the temperature adjustment variable resistor is zero ohms and at a low temperature when the resistance of the temperature adjustment variable resistor is maxium. The minimum temperature preset in actual practice, however, tends to depart from a constant value due to fluctuations of the resistance of the variable resistor. As a result, if the resistance of the variable resistor exceeds a certain limit when manipulating the variable resistor to a maximum, the temperature of the car interior becomes too low, and the evaporator of the cooling system is excessively cooled, resulting in frosting of the evaporator to disadvantageousl'y decrease the cooling capacity.

It is therefore an object of the present invention to provide an arrangement which substantially obviates one or more of the limitations and disadvantages of the described prior arrangements.

It is another object of the present invention to provide a control device for cooling systems so constructed as to render the temperature of the car interior to be at a minimum when the resistance of the temperature adjustment variable resistor is zero ohms to minimize deviations from the lowest temperature, thereby preventing the frosting of the evaporator.

Another object of the invention is to provide a control device practically suitable for use in cooling systems of automobiles having a comparatively small engine, by combining the afore-said temperature control circuit with an engine speed detecting circuit for the cooperative control of the refrigerator by these two circuits to disconnect the refrigerator from the engine during low-speed running in order to prevent the engine from being overloaded.

SUMMARY OF THE INVENTION There has been provided a control device for the cooling system of an automobile which is mechanically coupled thereto, including a temperature sensitive circuit with a variable resistor, having a movable intermediate terminal and a heat sensitive resistor serially coupled to said resistor for producing a voltage signal at said intermediate terminal indicative of the temperature of said heat sensitive elements. A transistor circuit including first and second transistors of the same conductivity type, produce a control signal for engaging and disengaging the magnetic clutch in response to an output of said variable resistor as determined in accordance with the position of said movable intermediate terminal. A feedback circuit is coupled between the output of said transistor circuit and the connection of said variable resistor and said heat sensitive element for changing the quantity of current fed back through said feedback resistor with the change in resistance of said variable resistor, thereby preventing any substantial change in hysteresis temperature width as a function of the operation temperature ranges, as detennined by said variable resistor.

For a better understanding of the present invention, together with other and further objects thereof, reference is directed to the following description, taken in connection with the accompanying drawings while its scope will be pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a circuit diagram illustrating one embodiment of the invention;

FIG. 2 shows wave forms for voltages across various parts of an engine speed detector of the control device according to the invention;

FIG. 3 is a plot for the temperature-resistance characteristic of a heat-sensitive element in the temperature control circuit of the control device according to the invention; and

FIG. 4 is a graph showing the relation between angle of rotation and temperature of the temperature adjustment variable resistor in the control device according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The invention is now described in conjunction with an illustrated embodiment thereof. Referring now to FIG. 1, there are shown a d-c source 1, an ignition coil 2, a distributor switch contact 3, and a control device 4 according to the invention, with an engine speed detector input terminal indicated at 4a, an earth terminal at 4b, a source terminal at 40, an output terminal at 4d, a temperature detecting input terminal at 4e, and a feedback terminal at 4f. An electromagnetic clutch 5 is connected between the output terminal 4d and earth for switching the connection between the cooling system (not shown) and an engine driving the cooling system. A temperature adjustment variable resistor 6 is connected between the terminal 4e and a temperature detecting thermistor 7 having a grounded terminal. The connection between the variable resistor 6 and the thermistor 7 is connected to the feedback terminal 4f.

The input terminal 4a is connected through resistors 8 and 9 to the base of a transistor 12, to which base is also connected a resistor 11 which has the other terminal connected to the ground terminal 4b. The connection between the resistors 8 and 9 is connected through a capacitor to the earth terminal 4b. The emitter of the transistor 12 is connected through a resistor 14 to the earth terminal 4b.

To the collector of the transistor 12 are connected'a resistor 13 and a capacitor 15, with the other terminal of the resistor 13 connected to the source terminal 40 and the other terminal of the capacitor 15 connected together with a resistor 16 to the base of a transistor 17, which has the emitter connected through a diode 19 to the earth terminal 4b and the collector connected to a resistor 18, a capacitor 20 and a resistor 21. The other end of the resistor 18 is connected to the source terminal 4c, the other end of the capacitor 20 is connected directly to the earth terminal 4b, and the other end of the resistor 21 is connected through a variable resistor 22 and a resistor 23 to the earth terminal 4b. The slidable tap of the variable resistor 22 is connected to the base of a transistor 24, which has the emitter connected through resistors 32 and 33 to the earth terminal common to the emitter of a transistor 31 and the collector connected to a resistor 38, the base of the transistor 31 and the collector of a transistor 30. The other end of the resistor 38 is connected to the source terminal 40. The transistor 30 has the base connected through a resistor 29, a variable resistor 28, a resistor 27 and a resistor 25 to the source terminal 4c. Between the connection between the resistors 25 and 27 and the earth terminal 4b is connected a Zener diode 26, and the connection between the variable resistor 28 and the resistor 29 is connected to the temperature detecting input terminal 4e. The emitter of the transistor 30 is connected to the connection between the resistors 32 and 33. The collector of the transistor 31 is connected to a coil 34a of a relay 34, a diode 36 and to a resistor 35. The other ends of the diode 36 and the coil 34a are respectively connected to the source terminal 40, and the other end of resistor is connected through a feedback resistor 39 to the feedback terminal 4f. The connection between the resistors 35 and 39 is connected through a capacitor 37 to the earth terminal 4b. The relay 34 has a relay contact 34b inserted between the source terminal 40 and the output terminal 4d.

The operation of the foregoing circuit construction will now be described. The function of the engine speed detecting circuit is first described. The action of the distributor switch contact 3, which is opened and closed in accordance with the engine rotation, produces a pulse train as shown at (a) in FIG. 2 across the terminals 4a and 4b. The pulse frequency and pulse width change with the engine rotation. In FIG. 2 the ordinate represents voltage V and the abscissa represents time t. The resistors 8, 9, ll, 13 and 14, the capacitor 10 and the transistor 12 constitute a pulse shaping circuit producing square-wave pulses as shown at (b) in FIG. 2 between the collector of the transistor 12 and the earth terminal 4b. A differentiating circuit constituted by the capacitor 15 and the resistor 16 renders the waveform of the signal across the ends of the resistor 16 into the one as shown at (c) in FIG. 2. A further pulse shaping circuit consisting of the transistor 17, the resistor 18 and the diode 19 would produce a signal of a waveform as shown at (d) in FIG. 2 between the collector of the transistor 17 and the earth terminal 4b if the capacitor 20 was not connected in the circuit as shown. The pulse width z is independent of the number of pulses per unit time and is constant. Thus, it is possible to obtain a pulse signal whose recurring frequency changes with the engine rotation, but which has a constant pulse width. Accordingly, the number of the pulses having a constant pulse width increases with the increasing number of engine rpm. The voltage across the terminals of the integrating capacitor 20 connected between the collector of the transistor 17 and the earth terminal 4b is indicated by a dashed line at (d) in FIG. 2. With an increase in the number of the pulses of constant pulse width T the terminal voltage across the integrating capacitor 20 decreases, and conversely with a decrease in the number of the pulses the terminal voltage across the integrating capacitor 20 increases. When the base potential for the transistor 24 decreases as a result of decrease of the terminal voltage of the integrating capacitor 20, the collector-emitter path of the transistor 24 is cut-off, and the base current enters from the source through the resistor 38 into the transistor 31 to trigger the transistor 31 so as to close the contact 34b of the relay 34, thus actuating the electromagnetic clutch 5. It will be apparent that the electromagnetic clutch 5 is not operated during low-speed engine operation until a speed determined by the variable resistor 22 is reached, whereupon the electromagnetic clutch 5 is operated to start the cooling system operation. Therefore, for an automobile having a sm allsize engine whose output becomes in sufficient during low-speed operation, the cooling system is automatically disconnected from the engine during low-speed operation to lessen the burden on the engine thus aiding the smooth running of the automobile.

Next, the function of the temperature control circuit is described in detail. The thermistor 7 is installed in the neighborhood of an evaporator of the cooling system (not shown). It is held in a low resistance state at a high ambient temperature. When the temperature adjustment variable resistor 6 is preset to zero ohms, the base potential of the transistor 30 is low so long as the resistance of the thermistor 7 is low as just described, so that the transistor 30 is cut-off. As a result, current from the source 1 enters through the resistor 38 into the base of the transistor 31 to be carried out by the transistor 31, causing current through the coil 34a of the relay 34 to excite the coil 34a, thereby closing the contact 34b of the relay 34. Thus, the clutch 5 is operated to actuate the cooling system, thus gradually decreasing the temperature of the surroundings around the thermistor. As the collector of the transistor 31 is at this time substantially at earth potential (since the resistances of the resistors 32 and 33 are sufficiently low as compared to the d-c resistance of the coil 34a), the feedback resistor 39 can be regarded as being connected in parallel with the thermistor 7, with one terminal of the feedback resistor 39 being grounded through the resistor 35 and the collector-to-emitter path of the transistor 31. When the ambient temperature around the thermistor 7 7 falls to reach t in FIG. 3 (where the ordinate is taken for the resistance R of the thermistor 7 and the abscissa is taken for the temperature 1 around the thermistor), the resistance of the thermistor 7 becomes R By setting such that the resistance of the resistor 35, being omitted from the above equation from the relation R R where V, is the Zener voltage for the Zener diode 26, V is the base potential for the transistor 30 when it carries current through collector and emitter, R is the resistance of the resistor 27, R is the resistance of the variable resistor 28, and R is the resistance of the feedback resistor 39, the transistor 30 carries current while the transistor 31 is cut-off. As a result, the excitation of the coil 34a of the relay 34 is stopped to open the contact 34b of the relay 34, thus restoring the operative state of the electromagnetic clutch 5 so as to stop the operation of the cooling system, so that the ambient temperature around the thermistor, i.e., the eventual car interior temperature, begins to rise. At the instance of cut-off of the transistor 31 the collector potential for the transistor 31 increases substantially to the source potential. Current from the source 1 through the feedback resistor 39 enters the base of the transistor 30 in addition to current supplied from point A through the resistors 27 and 28, so that the transistor 30 is not cutoff if the resistance of the thermistor 7 is reduced from the aforesaid value of R, with an increase in the ambient temperature until a resistance R of the thermistor 7 is reached. For the thermistor resistance R, the ambient temperature around the thermistor 7 is with t, At being the hysteresis temperature width.

As is described the lowest temperature I, of the car interior when the temperature adjustment variable resistor 6 is zero ohms is determined in the foregoing manner, and by increasing the angle of rotation of the temperature adjustment variable resistor 6 to increase the resistance thereof the transistor 30 may be triggered before the afore-said resistance R, of the thermistor 7 is reached, so that operation of the electromagnetic clutch 5 is stopped to gradually increase the temperature of the car interior. Determination of the lowest car interior temperature when the temperature adjustment variable resistor 6 is zero ohms makes it possible to exactly predetermine the lowest temperature of the car interior, independently of the fluctuations of the resistance of the variable resistor 6. Although there takes place a deviation from a preset temperature at a higher range due to fluctuations of the resistance of the temperature adjustment variable resistor 6, such deviation will not lead to the frosting of the evaporator and not cause any practical problems.

Means for obtaining the afore-mentioned hysteresis temperature width include a known Schmitt circuit using a common-emitter resistor and a method wherein the feedback resistor 39 of the device according to the invention is connected to the terminal 4e. The latter method has entirely the same effects when the resistance of the temperature adjustment variable resistor 6 is zero ohms. In other words, when the resistance of the temperature adjustment variable resistor 6 is zero ohms i.e., at a minimum, the resistance of the thermistor 7 takes a maximum value of R corresponding to the lowest ambient temperature of t,,, as the voltage dividing resistance capable of attaining a base potential V at which the transistor 30 is triggered is constituted by the sum of the series resistances of the temperature adjustment variable resistor 6 and of the thermistor 7, whereas when the resistance of the temperature adjustment variable resistor 6 is maximum, the above base voltage V is reached with a low resistance of the thermistor 7, i.e., R (corresponding to an ambient temperature t around the thermistor 7). In this manner the ambient temperature may be adjusted by means of the temperature adjustment variable resistor 6 in a range between t, and 1 If the feedback resistor 39 is connected to the terminal 4e, however, an extremely broad hysteresis temperature width results when the resistance of the temperature adjustment variable resistor 6 assumes a maximum value R,,,,, to the disadvantage of the operation of the system.

The resistance-temperature characteristic of the thermistor 7 has a steep slope in a high resistance region and a gradual slope in a low resistance region. As R R R for the case where the feedback is connected directly to 4e, the quantity of current fed through the feedback resistor 39 back to the base of the transistor 30 is exactly the same both when the resistance of the temperature adjustment variable resistor 6 is zero ohms corresponding to a thermistor resistance of R and when the temperature adjustment variable resistor 6 has the maximum resistance R corresponding to a thermistor resistance R Equation is valid for the width of the hysteresis resistance, so that the transistor 30 is not cut-off until the resistance of the thermistor 4 reaches R corresponding to an ambient temperature t with t t t which is a disadvantage. Results of experiments reveal that by setting t to be +15 C when t, is -3 C, t;, is 0 C and At is 3 C, t is +24 C. for the case where the feedback is connected directly to 4e. At the same time, At' is 9 C, with At'lAt being 3. Thus, setting the resistance of the temperature adjustment variable resistor 6 to a maximum disadvantageously results in an extremely broad hysteresis temperature width in the high temperature region. This disadvantage of a broad hysteresis temperature width in the high temperature region also results from the use of the Schmitt circuit as the quantity of current fed back depends upon the common emitter resistor.

In the control device according to the invention, therefore, the cut-off of the transistor 30 is promoted (by positive feedback) so that it is cut-off early, even when the resistance of the thermistor 7 is low, that is, when the resistance of the temperature adjustment variable resistor 6 is high, by reducing the quantity of the current fed back through the feedback resistor 39, which desirable object is attained by connecting one end of the resistor 39 to the connection between the temperature adjustment variable resistor 6 and the thermistor 7 so as to feed the base current through the temperature adjustment variable resistor 6 to the transistor 30. Thus, it is possible to decrease the current fed back when the resistance of the temperature adjustment variable resistor 6 is high, i.e., when the resistance and the value of resistance per unit degrees of centigrade temperature of the thermistor 7 are low, and it is possible to increase the current fed back when the resistance of the temperature adjustment variable resistor 6 is low, i.e., when the resistance and the value of resistance per unit degrees centigrade of temperature of the thermistor 7 are high. This has the outstanding advantage of obtaining a required hysteresis temperature width at any angle of rotation of the temperature adjustment variable resistor 6.

As a consequence, the electromagnetic clutch 5 becomes inoperative at temperature 17 and operative at temperature 1 when the resistance of the temperature adjustment variable resistor 6 is maximum, and the hysteresis temperature difference t t in the high temperature region is equal to the hysteresis temperature difference, t t,,, in the low temperature region. F IG. 4 shows the relationship between rotation angle and temperature T of the temperature adjustment variable resistor 6. A indicates the instant when the operation of the electromagnetic clutch 5 is started, and B indicates an instant when the operation of the electromagnetic clutch 5 is stopped. M indicates the maximum rotation angle. The potential at point A in FIG. 1 is determined by the Zener voltage for the Zener diode 26, so there is no voltage variation. Thus, the control device according to the invention is substantially free from variation of the preset temperature due to variation of the source voltage. Further, the resistor 35 and the capacitor 37 constitute a filter circuit for avoiding the influence of, noise pulses from the ignition apparatus acting upon the temperature control circuit.

In the foregoing circuit construction the resistors 32 and 33 serve to impart a hysteresis characteristic to the switching function of the transistor circuit consisting of the transistors 24 and 31 with respect to the output signal from the engine speed detecting circuit. Also, one of the resistors 32 and 33, namely resistor 33, adjusts the hysteresis characteristic of the switching function of the transistor circuit consisting of the transistors 30 and 31 to enable adjustment of the hysteresis temperature difference between A and B as shown in FIG. 4. This means that the adjustment of the afore-said hysteresis temperature difference between A and B may be attained by the resistor 33 as well as by the feedback resistor 39. Further, similar to the known Schmitt circuit, the resistor 33 serves to increase the speed of switching of the afore-said transistor circuit with respect to a slow change in resistance of the thermistor 7.

While there has been described what a present is considered to be the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein, without departing from the invention, and it is therefore aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

I claim 1. A control device for use with an automobile cooling system which is operatively coupled to a driving source in accordance with a control output signal of said control device, comprising:

a temperature sensitive circuit including a series circuit of a temperature adjustment variable resistor having a movable intermediate terminal and a temperature detecting heat-sensitive element for producing a voltage signal at said intermediate terminal indicative of a selected temperature at a selected position;

a transistor circuit including first and second transistors of the same conductivity-type, each including a base emitter and collector,

said first transistor having its base connected to said intermediate terminal and being rendered nonconductive when said voltage signal indicates that the temperature at said position exceeds a predetermined value, thereby producing a signal ac the collector of said first transistor,

said second transistor having its base connected to the collector of said first transistor and being rendered conductive for producing said control output signal when said first transistor produces said signal at its collector; and

a feedback resistor connected to said collector of said second transistor and a connection between said variable resistor and said heat-sensitive element coupled to the other end of said feedback resistor for changing the quantity of current fed back through said feedback resistor with the change in resistance of said variable resistor thereby preventing any substantial change in hysteresis temperature width as a function of operation temperature ranges as determined by said variable resistor.

2. A control device for an automobile cooling system which is operatively coupled to a driving source in accordance with a control output signal of said control device, comprising:

an engine speed detecting circuit including:

a pulse shaping circuit for shaping pulses generated in correspondence with the engine r.p.m.,

a pulse differentiating shaping circuit for differentiating output pulses from said first-mentioned shaping circuit to produce shaped pulses having a constant pulse width, and

an integrating circuit for integrating said constantwidth pulses to produce a first voltage signal corresponding to the engine r.p.m.,

a temperature sensitive circuit including a series circuit of a variable resistor having a movable intermediate terminal and a heat-sensitive resistor located at a given position for producing a second voltage signal at said intermediate terminal indicative of a temperature at said position;

a transistor circuit including first, second and third transistors of the same conductivity-type each including a base, collector and emitter,

said first transistor having its base connected to said intermediate terminal and being rendered nonconductive when said second voltage signal indicates that the temperature at said position exceeds a predetermined value, thereby producing a signal at the collector of said first transistor,

said third transistor having its base connected to said integrating circuit and being rendered non-conductive when said first voltage signal indicates that the engine -r.p.m. exceeds a predetermined value, thereby producing a signal at the collectorof said third transistor,

said second transistor having its base connected to the collectors of said first and third transistors and being rendered conductive for producing said control output signal when both said first and third transistors produce said signals at their collectors; and

a feedback resistor having one end connected to the collector of said second transistor and a connection between said variable resistor and said heatsensitive element coupled to the other end of said feedback resistor for changing the quantity of current fed back through said feedback resistor with a change in resistance of said variable resistor thereby preventing any substantial change in hysteresis temperature width as a function of operation temperature ranges as determined by said variable resistor, said series transistor circuit being constructed to cause the cooling system operation to start only when both the output signal from said engine speed detecting circuit and the output signal from said temperature detecting circuit reach respective selected values.

3. A control system for use in controlling an automobile cooling system to an engine of the automobile said control system comprising:

a series circuit of a variable resistance and a temperature-sensitive resistance connected to a power source for providing a bias signal across said series circuit which bias signal may be used to provide a control signal for the input of said control means.

said bias signal causing actuation/deactuation of said cooling system at relatively low temperature ranges for low resistance values of said variable resistance and at relatively high temperature ranges for high resistance values of said variable resistance, and positive feedback resistor for causing hysteresis between actuation a'nd deactuation temperature for said cooling system said feedback resistor being connected from an output of said control means to the junction of said variable resistor and said temperature-sensitive resistance whereby the amount of positive feedback at said high temperature ranges is automatically reduced in comparison with the amount of positive feedback at said low temperature ranges by virtue of the respective high and low resistance values for said variable resistor thereby preventing substantial changes in said hysteresis as a function of operation temperature ranges which might otherwise be caused by non-linear characteristics of said temperature-sensitive resistance.

4. A control system as in claim 3 further comprising engine speed responsive means connected to the input of said control means for causing deactuation of said cooling system when the engine speed decreases below a predetermined value.

Patent No. Dated August 9, 1972 Inventor(s) Hisashi YQNEZU It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the heading, under "Foreign Application Priority Data" read "May 5, 1969" as May 6, 1969 Signed and Sealed this 13th day of Peliruary 1973 (SEAL) Attest:

EDWARD M. FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. Dated August 29, 1972 Inventor(s) Hisashi YDNEZU It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the heading, under "Foreign Application Priority Data" read "May 5, 1969" as May 6, 1969 Signed and sealed this 13th day of February 1973..

(SEAL) Attest:

EDWARD M. FLETCHER,JR. ROBERT GOTTSCHALK Atteeting Officer Commissioner of Patents 

1. A control device for use with an automobile cooling system which is operatively coupled to a driving source in accordance with a control output signal of said control device, comprising: a temperature sensitive circuit including a series circuit of a temperature adjustment variable resistor having a movable intermediate terminal and a temperature detecting heatsensitive element for producing a voltage signal at said intermediate terminal indicative of a selected temperature at a selected position; a transistor circuit including first and second transistors of the same conductivity-type, each including a base emitter and collector, said first transistor having its base connected to said intermediate terminal and being rendered non-conductive when said voltage signal indicates that the temperature at said position exceeds a predetermined value, thereby producing a signal ac the collector of said first transistor, said second transistor having its base connected to the collector of said first transistor and being rendered conductive for producing said control output signal when said first transistor produces said signal at its collector; and a feedback resistor connected to said collector of said second transistor and a connection between said variable resistor and said heat-sensitive element coupled to the other end of said feedback resistor for changing the quantity of current fed back through said feedback resistor with the change in resistance of said variable resistor thereby preventing any substantial change in hysteresis temperature width as a function of operation temperature ranges as determined by said variable resistor.
 2. A control device for an automobile cooling system which is operatively coupled to a driving source in accordance wiTh a control output signal of said control device, comprising: an engine speed detecting circuit including: a pulse shaping circuit for shaping pulses generated in correspondence with the engine r.p.m., a pulse differentiating shaping circuit for differentiating output pulses from said first-mentioned shaping circuit to produce shaped pulses having a constant pulse width, and an integrating circuit for integrating said constant-width pulses to produce a first voltage signal corresponding to the engine r.p.m., a temperature sensitive circuit including a series circuit of a variable resistor having a movable intermediate terminal and a heat-sensitive resistor located at a given position for producing a second voltage signal at said intermediate terminal indicative of a temperature at said position; a transistor circuit including first, second and third transistors of the same conductivity-type each including a base, collector and emitter, said first transistor having its base connected to said intermediate terminal and being rendered non-conductive when said second voltage signal indicates that the temperature at said position exceeds a predetermined value, thereby producing a signal at the collector of said first transistor, said third transistor having its base connected to said integrating circuit and being rendered non-conductive when said first voltage signal indicates that the engine r.p.m. exceeds a predetermined value, thereby producing a signal at the collector of said third transistor, said second transistor having its base connected to the collectors of said first and third transistors and being rendered conductive for producing said control output signal when both said first and third transistors produce said signals at their collectors; and a feedback resistor having one end connected to the collector of said second transistor and a connection between said variable resistor and said heat-sensitive element coupled to the other end of said feedback resistor for changing the quantity of current fed back through said feedback resistor with a change in resistance of said variable resistor thereby preventing any substantial change in hysteresis temperature width as a function of operation temperature ranges as determined by said variable resistor, said series transistor circuit being constructed to cause the cooling system operation to start only when both the output signal from said engine speed detecting circuit and the output signal from said temperature detecting circuit reach respective selected values.
 3. A control system for use in controlling an automobile cooling system to an engine of the automobile said control system comprising: a series circuit of a variable resistance and a temperature-sensitive resistance connected to a power source for providing a bias signal across said series circuit which bias signal may be used to provide a control signal for the input of said control means. said bias signal causing actuation/deactuation of said cooling system at relatively low temperature ranges for low resistance values of said variable resistance and at relatively high temperature ranges for high resistance values of said variable resistance, and a positive feedback resistor for causing hysteresis between actuation and deactuation temperature for said cooling system said feedback resistor being connected from an output of said control means to the junction of said variable resistor and said temperature-sensitive resistance whereby the amount of positive feedback at said high temperature ranges is automatically reduced in comparison with the amount of positive feedback at said low temperature ranges by virtue of the respective high and low resistance values for said variable resistor thereby preventing substantial changes in said hysteresis as a function of operation temperature ranges which might otherwise be caused by non-linear characteristics of said temperature-sensitive resistance.
 4. A control system as in claiM 3 further comprising engine speed responsive means connected to the input of said control means for causing deactuation of said cooling system when the engine speed decreases below a predetermined value. 